The peregrine falcon (Falco peregrinus) is a cosmopolitan raptor celebrated as the fastest animal on Earth. In its hunting dive, or stoop, it can exceed 300 kilometres per hour. An apex aerial predator, it feeds almost entirely on other birds, which it strikes in mid-flight with a clenched foot. Historically the species inhabited every continent except Antarctica, nesting on high cliff ledges and, occasionally, on tall built structures. Long prized by falconers for its speed and trainability, the peregrine's broad distribution and adaptability made it, until the middle of the twentieth century, a familiar sight across much of North America and Eurasia.
In the decades after the Second World War, peregrine populations collapsed across much of their range. Investigators eventually attributed the decline to DDT, a synthetic pesticide that concentrated in the birds' tissues as it moved up the food chain, a process termed bioaccumulation. The compound disrupted the females' calcium metabolism, causing them to lay abnormally thin-shelled eggs that cracked beneath the incubating parent. Reproduction all but ceased. By the early 1970s the peregrine had been extirpated from the entire eastern United States and was regarded as endangered throughout its former territory — a startling reversal of fortune for so widespread and capable a bird.
The prohibition of DDT in the early 1970s removed the principal threat, yet the depleted populations could not recover unaided. Conservationists therefore launched ambitious captive-breeding programmes, rearing chicks in incubators and returning them to the wild through hacking, a centuries-old falconry method in which fledglings are gradually acclimatized from an elevated release box. Over roughly two decades, several thousand captive-bred birds were introduced across the continent. The undertaking proved remarkably effective: by 1999 the species had rebounded sufficiently for authorities to remove it from the United States endangered-species list, an outcome few observers had thought possible a single generation earlier.
One of the peregrine's most dependable modern strongholds is, improbably, the city. Skyscrapers imitate the sheer cliff ledges the birds instinctively favour, and urban districts teem with pigeons, a plentiful year-round prey. Breeding pairs now raise their young on office towers, bridges, and cathedral spires in dozens of cities, frequently observed by webcams that have turned the falcons into unlikely local celebrities. Some biologists caution that urban living carries hazards of its own, chiefly collisions with glass and traffic, which kill many young birds in their first year. Even so, few dispute that the peregrine's rescue ranks among the signal achievements of twentieth-century conservation.